Examples of conventional electric motors are described in Japanese Patent Application Laid-Open Publication No. 2007-202391; Japanese Patent Application Laid-Open Publication No. 2007-143278; and Japanese Patent Application Laid-Open Publication No. 2010-93977. The electric motor described in each of Japanese Patent Application Laid-Open Publication No. 2007-202391 and Japanese Patent Application Laid-Open Publication No. 2007-143278 is an electric motor with brush, provided with: a magnet (stator) serving as a field fixed to a case; and a rotor serving as an armature rotatably provided in the case. Furthermore, the electric rotor is provided with: a core around which coils is wound; and a commutator connected to the coil. In addition, the electric rotor is further provided with: a common brush which contacts the commutator; a low-speed-driving brush; and a high-speed-driving brush.
The brushes are disposed in the phases mutually different in the rotation direction of the electric rotor, and switching elements are provided at the respective paths which supply electric power to the brushes. When the switching elements are turned on or off, the brush to supply a current is switched, and the rotation number of the electric rotor is controlled to a low speed or a high speed.
The motor described in Japanese Patent Application Laid-Open Publication No. 2010-93977 is not provided with a brush, but is provided with a stator (stationary part), which is serving as an armature in a case, and a rotor serving as a field rotatably provided in the case. The stator has a stator core and a coil wound around the stator core. The coil has three coils to which excitation currents of three phases, in other words, a U-phase, a V-phase, and a W-phase are supplied, and the coils are disposed so that the phases are mutually shifted in the rotation direction of the rotor.
Furthermore, it is provided with switching elements electrically connected to the respective coils. By alternately switching on/off of the switching elements and controlling duty ratios, which are the rate of “on”, currents are supplied to all the coils with shifted timing, and the rotation number of the rotor is controlled.
On the other hand, one example of a conventional motor apparatus is described in Japanese Patent Application Laid-Open Publication No. 2003-47277. The motor apparatus described in Japanese Patent Application Laid-Open Publication No. 2003-47277 is provided with a brushless motor, an inverter circuit, a control circuit, a speed control arithmetic unit, etc. The brushless motor has: a rotor to which permanent magnets and a sensor magnet are attached; and a stator provided in the outer peripheral side of the rotor. The stator ha: a core which is a stack of steel plates or the like; and three coils corresponding to three phases, in other words, a U-phase, a V-phase, and a W-phase wound around the core.
Furthermore, the inverter circuit is used for connecting/shutting-off the three coils and an electric power source, and it is provided with positive-electrode switching elements and negative-electrode switching elements corresponding to the U-phase, the V-phase and the W-phase. Furthermore, the control circuit separately turns on/off the switching elements.
Furthermore, based on the intensity of the magnetic field formed by the sensor magnet, three sensors which output signals are provided to correspond to the U-phase, the V-phase, and the W-phase. The three sensors are disposed at an interval of a mechanical angle 120° outside the sensor magnet. Furthermore, the signals output from the sensors are input to the speed control arithmetic unit, and the speed control arithmetic unit controls on/off of the switching elements of the inverter circuit.
In the motor apparatus described in Japanese Patent Application Laid-Open Publication No. 2003-47277, on/off of the switching elements is controlled, currents are supplied to the three coils at predetermined timing, and a rotating magnetic field is formed by the three coils to rotate the rotor. Furthermore, the speed control arithmetic unit detects the rotation phases of the rotor on the basis of the signal output from the singe sensor determined in advance among the three sensors and, on the basis of the detected rotation phase, controls the on/off timing of the switching elements.
Therefore, even if there are errors in the attachment positions of the other two sensors with respect to the single sensor determined in advance, it is assumed that electric power can be distributed to the three coils at ideal energization timing, and the rotation number of the rotor can be appropriately controlled.